Many diverse diseases arise from an excess of unfolded proteins in the endoplasmic reticulum (ER stress). ER stress induces the unfolded protein response (UPR), in which numerous protective genes are activated. It is critical to understand how the UPR defends against ER stress, and how UPR signaling affects other cellular processes. While three canonical UPR transcription factors have been identified, we have determined in C. elegans that the transcription factor SKN-1 (mammalian Nrf1/2/3) is also central to the UPR. SKN-1 has a conserved function in oxidative stress defense, and is important in longevity. We have shown that SKN-1 is regulated by the UPR, and is needed for ER stress to activate core UPR regulators, as well as downstream effector genes. Surprisingly, UPR signaling is required for SKN-1 to respond to oxidative stress, which suggests that ER signaling may broadly influence cellular stress defenses, and may regulate SKN-1 in the insulin-IGF-1-like signaling (IIS) and TOR (target of rapamycin) pathways. Using the powerful C. elegans model, this project will investigate: (1) how and in what tissues SKN-1 defends against ER stress, and how IIS and TOR might affect ER stress resistance through SKN-1, (2) how SKN-1 is regulated by the UPR during ER stress, oxidative stress, and in the context of the IIS and TOR pathways, and (3) what genes and biological processes are controlled directly by SKN-1 during the UPR. Transgenic, genetic, molecular, cell biological, and chromatin immunoprecipitation (ChIP) approaches will be used to investigate how SKN-1 functions are regulated by the UPR and contribute to ER stress resistance in vivo. A proven RNAi screening strategy will identify new regulators of SKN-1 during ER stress, and high-throughput sequencing combined with expression profiling and ChIP will be employed to identify genes and processes regulated directly by SKN-1. These studies will provide important and novel insights into how the ER defends itself against stress, and will substantially alter paradigms for understanding ER-based signaling and how it influences other cellular defense mechanisms.